1// Copyright (c) 2011 The Chromium Authors. All rights reserved. 2// Use of this source code is governed by a BSD-style license that can be 3// found in the LICENSE file. 4 5#ifndef BASE_WIN_OBJECT_WATCHER_H_ 6#define BASE_WIN_OBJECT_WATCHER_H_ 7 8#include <windows.h> 9 10#include "base/base_export.h" 11#include "base/callback.h" 12#include "base/memory/weak_ptr.h" 13#include "base/message_loop/message_loop.h" 14 15namespace base { 16namespace win { 17 18// A class that provides a means to asynchronously wait for a Windows object to 19// become signaled. It is an abstraction around RegisterWaitForSingleObject 20// that provides a notification callback, OnObjectSignaled, that runs back on 21// the origin thread (i.e., the thread that called StartWatching). 22// 23// This class acts like a smart pointer such that when it goes out-of-scope, 24// UnregisterWaitEx is automatically called, and any in-flight notification is 25// suppressed. 26// 27// Typical usage: 28// 29// class MyClass : public base::ObjectWatcher::Delegate { 30// public: 31// void DoStuffWhenSignaled(HANDLE object) { 32// watcher_.StartWatching(object, this); 33// } 34// virtual void OnObjectSignaled(HANDLE object) { 35// // OK, time to do stuff! 36// } 37// private: 38// base::ObjectWatcher watcher_; 39// }; 40// 41// In the above example, MyClass wants to "do stuff" when object becomes 42// signaled. ObjectWatcher makes this task easy. When MyClass goes out of 43// scope, the watcher_ will be destroyed, and there is no need to worry about 44// OnObjectSignaled being called on a deleted MyClass pointer. Easy! 45// If the object is already signaled before being watched, OnObjectSignaled is 46// still called after (but not necessarily immediately after) watch is started. 47// 48class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver { 49 public: 50 class BASE_EXPORT Delegate { 51 public: 52 virtual ~Delegate() {} 53 // Called from the MessageLoop when a signaled object is detected. To 54 // continue watching the object, StartWatching must be called again. 55 virtual void OnObjectSignaled(HANDLE object) = 0; 56 }; 57 58 ObjectWatcher(); 59 ~ObjectWatcher(); 60 61 // When the object is signaled, the given delegate is notified on the thread 62 // where StartWatching is called. The ObjectWatcher is not responsible for 63 // deleting the delegate. 64 // 65 // Returns true if the watch was started. Otherwise, false is returned. 66 // 67 bool StartWatching(HANDLE object, Delegate* delegate); 68 69 // Stops watching. Does nothing if the watch has already completed. If the 70 // watch is still active, then it is canceled, and the associated delegate is 71 // not notified. 72 // 73 // Returns true if the watch was canceled. Otherwise, false is returned. 74 // 75 bool StopWatching(); 76 77 // Returns the handle of the object being watched, or NULL if the object 78 // watcher is stopped. 79 HANDLE GetWatchedObject(); 80 81 private: 82 // Called on a background thread when done waiting. 83 static void CALLBACK DoneWaiting(void* param, BOOLEAN timed_out); 84 85 void Signal(Delegate* delegate); 86 87 // MessageLoop::DestructionObserver implementation: 88 virtual void WillDestroyCurrentMessageLoop(); 89 90 // Internal state. 91 WeakPtrFactory<ObjectWatcher> weak_factory_; 92 Closure callback_; 93 HANDLE object_; // The object being watched 94 HANDLE wait_object_; // Returned by RegisterWaitForSingleObject 95 MessageLoop* origin_loop_; // Used to get back to the origin thread 96 97 DISALLOW_COPY_AND_ASSIGN(ObjectWatcher); 98}; 99 100} // namespace win 101} // namespace base 102 103#endif // BASE_OBJECT_WATCHER_H_ 104